Craftsman leaf blower runs fine and then begins to surge and lose power

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Old 05-18-16, 03:07 PM
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Craftsman leaf blower runs fine and then begins to surge and lose power

I have a Craftsman 200 mph leaf blower. It's a few years old, but seems to have good compression. I got it when it wasn't working and put a new carb on it, which allowed it to start.

I got one of the spline carb adjustment tools for low and high speed running. I got it started today. It's a little finicky, but it runs. After warming it up, I adjusted the high and low speed screws with the spline tool (absolutely necessary in my book. I tried other stuff and it just didn't work). I set the low speed when it was idling with the speed lever set at about 1/3 to 1/2. Purred along nicely. Then I put the speed lever on high and adjusted the high speed screw. It was really screaming along. I can't imagine this thing having any higher RPM's. I will add that the adjustment range is VERY narrow 1/8 turn or less, I can't imagine just setting it while it's not running with ANY hope of it starting/running well.

Put it to work blowing leaves. After running at top speed for about 10 minutes it began to surge and slowly lose power. I'm sure it would have quit but listening to it I shut it down. Was I out of gas (which I'd mixed with a good quality synthetic 2 cycle oil at probably 1:25 ratio... a little rich perhaps)? NO, in fact when I took the gas cap off, there was plenty of gas, and in fact it was like opening an aerosol can, it was quite pressurized, and thankfully I opened it with the gas cap absolutely on top. Is THAT pressure supposed to be? I took out the spark plug. It was dry and a darker gray color but not burned or carboned up. It was clean and looked good.

So, my question for you small engine gurus: what's with the slow surging heading on the way to a kill after it's been running wide open for 5-10 minutes? Is the gas tank supposed to be pressurized for this machine. I suppose that's what priming it is all about, eh?
 
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Old 05-18-16, 05:30 PM
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My guess is your gas cap is defective. The gas tank pressure should be at or near atmospheric for the metering diaphragm in the carb to operate properly. As the gas in the tank heats up. it expands increasing the tank pressure. The next time you start experiencing the problem, remove the gas cap as a test.
 
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Old 05-18-16, 05:55 PM
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The screaming rpm and grey spark plug tell me that your engine is burning up. It can't run at that blazing rpm for long, it's running too lean. It may have galled the piston and/or cylinder and maybe stuck a ring, or it may not have yet but will if you keep adjusting the carb that way. The heat may have been enough to cause the pressure in the gas tank. When you adjust the engine to that highest possible rpm, continue to back the screw out until the engine just barely begins to flutter and leave it there. Otherwise is will be toast before long.
 
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